Noise measuring device and method, recording medium

ABSTRACT

A noise measuring unit  24  measures a noise power based on an output from a digitizer  16  and the amplification factor of a limiter amplifier  12  when an output from a device under test  10  is supplied for the digitizer  16  through the limiter amplifier  12 . Since the output from the device under test  10  is supplied through the limiter amplifier  12 , the noise component is sufficiently amplified, the carrier component saturates, and thus, the noise measuring unit  24  easily measures the noise power. At this time, the output frequency of the device under test  10  is not multiplied, and thus, it is not necessary to use a down converter or a spectrum analyzer, the C/N ratio can be measured at a high speed or with a simple constitution.

FIELD OF ART

[0001] The present invention relates to measuring the C/N ratio (Carrierto Noise ratio) of a signal provided from a DUT (Device Under Test).

BACKGROUND ART

[0002] Conventionally, the C/N ratio of a signal provided from a DUT(Device Under Test) has been measured, and a system configuration forthe measuring is shown in FIG. 7.

[0003] The frequency of a signal Fs provided from a DUT 102 ismultiplied by about a few tens by a multiplier 104. The frequency of asignal Fs×N provided from the multiplier 104 is reduced by a downconverter 106 down to a frequency which a digitizer 108 can process, andthen, the signal is supplied for the digitizer 108. The digitizer 108can measure the C/N ratio of the signal Fs×N provided from themultiplier 104. Note that since the C/N ratio is reduced by multiplyingthe frequency of the signal Fs provided from the DUT 102, the reducedamount is obtained by calculation, and the C/N ratio of the signal Fsprovided from the DUT 102 is obtained.

[0004] Alternately, the measuring system may be configured as shown inFIG. 8. Though this system is identical to the example above up to theprocess where the signal provided from the DUT 102 is multiplied byabout a few tens by the multiplier 104, the frequency of the signalprovided from the multiplier 104 is not reduced, and is processed by aspectrum analyzer 110. The C/N ratio of the signal Fs×N provided fromthe multiplier 104 can be measured by the spectrum analyzer 110. Notethat since the C/N ratio is reduced by multiplying the frequency of thesignal Fs provided from the DUT 102, the reduced amount is obtained bycalculation, and then, the C/N ratio of the signal Fs provided from theDUT 102 is obtained.

[0005] However, since the frequency which the digitizer 108 can handleis generally about a few tens of MHz, the down converter 106 isnecessary in the system shown in FIG. 7. The down converter 106 whichmeets such a high frequency signal as supplied from the multiplier 104is expensive, and its circuit is complex.

[0006] In the system shown in FIG. 8, since the processing speed of thespectrum analyzer 110 itself is generally slow, the overall processingspeed also is slow.

[0007] In view of the foregoing, the present invention has a purpose ofproviding an apparatus and the like which can measure the C/N ratioprovided from the DUT at a high speed or with a simple constitution.

DISCLOSURE OF THE INVENTION

[0008] According to an aspect of the present invention, a noisemeasuring apparatus includes: a limiter amplifying unit, that provides asignal to be measured in a predetermined range; and a digital dataconverting unit, that converts the output from the limiter amplifyingunit into digital data.

[0009] In the noise measuring apparatus constituted as described above,a carrier component in the output from the DUT is relatively largecompared with a noise component. Thus, if the limiter amplifying meansamplifies the output from the DUT, the noise component becomes larger.Additionally, since the signal after amplifying is provided in apredetermined range, the carrier component saturates, and does notbecome too large. Therefore, if the output from the limiter amplifyingmeans is converted into digital data by the digital data convertingmeans, since digital data with the increased noise component areobtained, measuring the noise component becomes easy. Consequently, thenoise component is measured at a high speed or with a simpleconstitution.

[0010] Note that the predetermined range generally means a one withdetermined upper limit and lower limit. However, the range may have onlya determined upper limit or lower limit if necessary.

[0011] The noise measuring apparatus according to the present inventionfurther includes a noise measuring unit, that measures noise based onthe output from the digital data converting unit and an amplificationfactor of the limiter amplifying unit.

[0012] The noise measuring apparatus according to the present inventionfurther includes a carrier digital data converting unit, that convertsthe output from the device under test into digital data.

[0013] The noise measuring apparatus according to the present inventionfurther includes an output switching unit, that supplies the digitaldata converting unit with the output from the limiter amplifying unit orthe output from the device under test, wherein the digital dataconverting unit also serves as the carrier digital data converting unit.

[0014] The noise measuring apparatus according to the present inventionfurther includes a carrier measuring unit, that measures the carrierbased on the output from the carrier digital data converting unit.

[0015] The noise measuring apparatus according to the present inventionfurther includes a noise measuring unit, that measures noise based onthe output from the digital data converting unit and the amplificationfactor of the limiter amplifying unit.

[0016] The noise measuring apparatus according to the present inventionfurther includes a C/N ratio calculating unit, that calculates a C/Nratio based on a measured result of the carrier measuring unit and thenoise measuring unit.

[0017] According to another aspect of the present invention, a noisemeasuring method includes: a limiter amplifying step of providing asignal to be measured in a predetermined range; and a digital dataconverting step of converting the output from the limiter amplifyingstep into digital data.

[0018] According to another aspect of the present invention, acomputer-readable medium has a program of instructions for execution bythe computer to perform a noise measuring process, the noise measuringprocess including: a limiter amplifying step of providing a signal to bemeasured in a predetermined range; and a digital data converting step ofconverting the output from the limiter amplifying step into digitaldata.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a block diagram showing a constitution of a noisemeasuring apparatus 1 according to an embodiment of the presentinvention;

[0020]FIG. 2 is a drawing showing an operation of a limiter amplifier12;

[0021] FIGS. 3 are drawings showing an operation of a digitizer 16, andinclude a drawing (FIG. 3(a)) showing a form of sampling an output froma DUT 10, and a drawing (FIG. 3(b)) showing a form of sampling an outputfrom the limiter amplifier 12;

[0022] FIGS. 4 are drawings showing a method of measuring power of acarrier signal, and include a drawing showing an output from thedigitizer 16 (FIG. 4(a)), a drawing showing separated carrier componentand noise component (FIG. 4(b)), a drawing showing the output from thedigitizer 16 transformed into the frequency domain (FIG. 4(c)), and adrawing showing a relationship between the actual frequency and thepower (FIG. 4(d));

[0023] FIGS. 5 are drawings showing a measuring method for noise power,and include a drawing showing the output from the digitizer 16 when itis assumed that the output from the limiter amplifier 12 is not limited(FIG. 5(a)), a drawing showing the output from the digitizer 16 when theoutput from the limiter amplifier 12 ranges from −L to L (FIG. 5(b)), adrawing showing the output from the digitizer 16 transformed intofrequency domain (FIG. 5(c)), and a drawing showing a relationshipbetween the actual frequency and the power (FIG. 5(d));

[0024]FIG. 6 is a flowchart showing an operation of the embodiment ofthe present invention;

[0025]FIG. 7 is a drawing showing a system constitution when the C/Nratio of the signal provided from the DUT is measured in prior art; and

[0026]FIG. 8 is a drawing showing another system constitution when theC/N ratio of the signal provided from the DUT is measured in prior art.

BEST MODE FOR CARRYING OUT THE INVENTION

[0027] The following section describes an embodiment of the presentinvention while referring to drawings.

[0028]FIG. 1 is a block diagram showing a constitution of a noisemeasuring apparatus 1 according to the embodiment of the presentinvention. The noise measuring apparatus 1 according to the embodimentof the present invention comprises a DUT (Device Under Test) 10, alimiter amplifier 12, a switch 14, a digitizer 16, and a C/N ratio(Carrier to Noise ratio) measuring unit 20.

[0029] The DUT 10 receives a signal to be measured which is not shown,and provides a signal corresponding to the signal to be measured.

[0030] The limiter amplifier 12 amplifies the output from the DUT 10,provides the amplified output, and provides a boundary value of a rangewhen the signal after the amplifying exceeds the range. The limiteramplifier 12 serves as limiter amplifying means. The following sectiondescribes the operation of the limiter amplifier 12 while referring toFIG. 2. First, a signal of a sinusoidal wave with the amplitude of A₀ issupplied for the limiter amplifier 12. It is assumed that theamplification factor of the limiter amplifier 12 is G. If the outputfrom the limiter amplifier 12 were not limited, the output would be asignal of a sinusoidal wave with an amplitude of GA₀. Further, when theoutput from the limiter amplifier 12 is limited to a range from −L to L,if the absolute value of the output exceeds L, the output is ±L, namelythe boundary value of the output range of the limiter amplifier 12. Whenthe absolute value of the output is L or less, the output remainsunchanged. Namely, if the input is A₀ sin ωt, the output from thelimiter amplifier 12 is:

GA₀ sin ωt(−L<GA₀ sin ωt<L),

L(L<GA₀ sin ωt), or

−L(GA₀ sin ωt<−L).

[0031] Note that in the example above, the upper limit (L) and the lowerlimit (−L) are specified for the output range of the limiter amplifier12. However, if the output from the device under test 10 is always equalto or more than 0, it is only necessary to specify the upper limit (L)for the range of the output from the limiter amplifier 12. Oppositely,if the output from the device under test 10 is always equal to or lessthan 0, it is only necessary to specify the lower limit (−L) for therange of the output from the limiter amplifier 12.

[0032] Returning to FIG. 1, the switch 14 connects the output from theDUT 10 or the output from the limiter amplifier 12 with the input to thedigitizer 16. The switch 14 has an input terminals 14 a and 14 b, and anoutput terminal 14 c. The input terminal 14 a is connected with theoutput from the DUT 10. The input terminal 14 b is connected with theoutput from the limiter amplifier 12. The output terminal 14 c isconnected with the input to the digitizer 16. The switch 14 connects theinput terminal 14 a and the output terminal 14 c with each other, or theinput terminal 14 b and the output terminal 14 c with each other.

[0033] The digitizer 16 converts the output from the switch 14 intodigital data, and provides the data. When the switch 14 connects theinput terminal 14 a and the output terminal 14 c with each other, thedigitizer 16 converts the output from the DUT 10 into digital data. Atthis time, the digitizer 16 serves as carrier digital data convertingmeans. When the switch 14 connects the input terminal 14 b and theoutput terminal 14 c with each other, the digitizer 16 converts theoutput from the limiter amplifier 12 into digital data. At this time,the digitizer 16 serves as digital data converting means.

[0034] The following section describes the operation of the digitizer 16while referring to FIG. 3. The digitizer 16 oversamples the output ofthe DUT 10 or the output of the limiter amplifier 12. For example, FIG.3(a) shows a form of sampling the output from the DUT 10, and FIG. 3(b)shows a form of sampling the output from the limiter amplifier 12 whenthe oversampling rate=4. The time interval of the sampling is ¼ of theperiod of the output from the DUT 10 or the output from the limiteramplifier 12. Namely, the frequency is four times. Note that thesampling of the output from the limiter amplifier 12 is conducted onlyin the neighborhood of the level 0 which is not clamped by the limiteramplifier 12. For example, the sampling is conducted only at points 100in FIG. 3(b).

[0035] While the digitizer 16 serves as the carrier digital dataconverting means and the digital data converting means, a digitizerserving as the carrier digital data converting means and a digitizerserving as the digital data converting means may be providedindependently.

[0036] The C/N ratio measuring unit 20 comprises a carrier measuringunit 22, a noise measuring unit 24, and a C/N ratio calculating unit 26.

[0037] The carrier measuring unit 22 measures the power of the carriersignal based on the output from the carrier digital data convertingmeans. Namely, it measures the power of the carrier signal based on theoutput from the digitizer 16 when the digitizer 16 converts the outputfrom the DUT 10 into the digital data.

[0038] The following section describes a measuring method for the powerof the carrier signal while referring to FIG. 4. FIG. 4(a) shows theoutput from the digitizer 16 when the digitizer 16 converts the outputfrom the DUT 10 into the digital data. As shown in FIG. 4(a), the outputfrom the digitizer 16 is a signal of the carrier signal superimposed bya minute noise. It is assumed that the frequency of the carriercomponent is fc. It is also assumed that the noise component has aconstant frequency, and the frequency of the noise component is fn. As aresult, as shown in FIG. 4(b), the output from the digitizer 16 isdivided into the carrier component (frequency: fc) and the noisecomponent (frequency fn). When the output from the digitizer 16 isFourier-transformed, and the powers for the respective frequencies areobtained, there exist powers at the frequency fc and the frequency fn asshown in FIG. 4(c). If the power at the frequency fc is Pc, and thepower at the frequency fn is Pn, the power of the carrier frequency isPc. Thus, the power of the carrier signal is obtained byFourier-transforming the output from the digitizer 16, and obtaining thepower at the frequency of fc. Note that since the frequency of the noisecomponent has a width, the actual relationship between the frequency andthe power takes the form shown in FIG. 4(d). However, the principle ofobtaining the power of the carrier signal remains the same. Also, sincethe amplitude of the noise signal is small as shown in FIG. 4(d), it isdifficult to measure it.

[0039] The noise measuring unit 24 measures the power of the noise basedon the output from the digital data converting means. Namely, the powerof the noise is measured based on the output from the digitizer 16 whenthe digitizer 16 converts the output from the limiter amplifier 12 intothe digital data.

[0040] The following section describes a measuring method for the powerof the noise while referring to FIG. 5. First, it is assumed that thefrequency of the carrier component is fc. It is also assumed that thenoise component has a constant frequency, and the frequency of the noisecomponent is fn. FIG. 5(a) shows the output from the digitizer 16 whenthe limiter amplifier 12 does not limit the output, and the digitizer 16converts the output from the limiter amplifier 12 into the digital data.Note that the output has already been divided into the carrier component(frequency: fc) and the noise component (frequency: fn) in the drawing.The noise component is multiplied by G/a compared with that of theoutput directly from the DUT 10. Note that (a) is an oversampling rateof the digitizer 16. However, since the carrier component is multipliedby G/a, the C/N ratio remains the same, and it is still difficult tomeasure the noise power.

[0041]FIG. 5(b) shows the output from the digitizer 16 when the outputof the limiter amplifier 12 ranges from −L to L, and the output from thelimiter amplifier 12 is converted into the digital data by the digitizer16. Though the carrier component saturates since the output is limitedto the predetermined range, the noise component does not saturate. Or,even if the noise component saturates, the degree of its saturation islower than that of the noise component. Note that though the L can bethe same as the amplitude A₀ of the carrier component, this value can beset arbitrarily as long as the limiter amplifier 12 is not damaged. Inthis way, when the carrier component saturates, the dynamic range formeasuring the noise power is multiplied by 2G/a compared with the casewhere the noise power is measured based on the output from the DUT 10.

[0042] Then, after the output from the digitizer 16 isFourier-transformed, and the powers are obtained for the respectivefrequencies, certain powers exist at the frequency of fc and thefrequency of fn as shown in FIG. 5(c). Here, the power at the frequencyof fn is (G/a).Pn. Thus, the power of the noise is obtained byFourier-transforming the output from the digitizer 16, obtaining thepower at the frequency of fn, and dividing the obtained value by G/a.Note that since the frequency of the noise component has a width, theactual relationship between the frequency and the power takes the formshown in FIG. 5(d). However, the principle of obtaining the noise powerremains the same.

[0043] The C/N ratio calculating unit 26 obtains the C/N ratio based onthe measured results from the carrier measuring unit 22 and the noisemeasuring unit 24. Specifically, the C/N ratio can be obtained bydividing the result measured by the noise measuring unit 24 by theresult measured by the carrier measuring unit 22.

[0044] The following section describes the operation of the embodimentof the present invention while referring to a flowchart in FIG. 6.First, the input terminal 14a and the output terminal 14 c are connectedwith each other in the switch 14, thereby supplying the digitizer 16with the output from the DUT 10 (S10). The digitizer 16 converts theoutput from the DUT 10 into the digital data (S12). Then, the carriermeasuring unit 22 measures the power of the carrier signal based on theoutput from the digitizer 16 (S14).

[0045] Then, the input terminal 14 b and the output terminal 14 c areconnected with each other in the switch 14, thereby supplying thedigitizer 16 with the output from the limiter amplifier 12 (S20). Thedigitizer 16 converts the output from the limiter amplifier 12 into thedigital data (S22). Then the noise measuring unit 24 measures the powerof the noise based on the output from the digitizer 16 (S24).

[0046] Finally, the C/N ratio calculating unit 26 obtains the C/N ratiobased on the measured results from the carrier measuring unit 22 and thenoise measuring unit 24 (S30). Specifically the C/N ratio is obtained bydividing the result measured by the noise measuring unit 24 by theresult measured by the carrier measuring unit 22.

[0047] With the present invention, the carrier component in the outputfrom the DUT 10 is relatively larger than the noise component.Therefore, if the limiter amplifier 12 amplifies the output from the DUT10, the noise component increases. In addition, when the signal afterthe amplifying exceeds the predetermined range (from −L to L), since theoutput is set to ±L, the carrier component saturates, and does notincrease too largely. Thus, after the output from the limiter amplifier12 is converted into digital data by the digitizer 16, since the digitaldata with the amplified noise component is obtained, measuring the noisecomponent becomes easy.

[0048] With the embodiment of the present invention, the power of thenoise component can be measured without multiplying the frequency of theoutput from the DUT 10. Thus, it is possible to measures the power ofthe noise component without a down converter or a spectrum analyzer.Therefore, the power of the noise component can be measured with aconstitution simpler than the down converter, or at a speed higher thanthe spectrum analyzer.

[0049] The embodiment described above can be realized as describedbelow. A media reading apparatus of a computer comprising a CPU, a harddisk, and the media (such as floppy disk and a CD-ROM) reading apparatusreads a medium recording a program for realizing the individual partsdescribed above, and the program is installed on the hard disk. Withthis method, the function described above can be realized.

[0050] With the present invention, the carrier component in the outputfrom the DUT is relatively larger than the noise component. Therefore,if the limiter amplifying means amplifies the output from the DUT, thenoise component increases. In addition, when the signal after theamplifying exceeds the predetermined range, since the output is set tothe boundary value of the range, the carrier component saturates, anddoes not increase too largely. Thus, after the output from the limiteramplifying means is converted into digital data by the digital dataconverting means, since the digital data with the amplified noisecomponent is obtained, measuring the noise component becomes easy.Consequently, the noise component can be measured at a high speed orwith a simple constitution.

1. A noise measuring apparatus comprising: a limiter amplifying unit,that provides a signal to be measured in a predetermined range; and adigital data converting unit, that converts the output from said limiteramplifying unit into digital data.
 2. The noise measuring apparatusaccording to claim 1 further comprising a noise measuring unit, thatmeasures noise based on the output from said digital data convertingunit and an amplification factor of said limiter amplifying unit.
 3. Thenoise measuring apparatus according to claim 1 further comprising acarrier digital data converting unit, that converts the output from saiddevice under test into digital data.
 4. The noise measuring apparatusaccording to claim 3 further comprising an output switching unit, thatsupplies said digital data converting unit with the output from saidlimiter amplifying unit or the output from said device under test,wherein said digital data converting unit also serves as said carrierdigital data converting unit.
 5. The noise measuring apparatus accordingto claim 3 further comprising a carrier measuring unit, that measuresthe carrier based on the output from said carrier digital dataconverting unit.
 6. The noise measuring apparatus according to claim 5further comprising a noise measuring unit, that measures noise based onthe output from said digital data converting unit and the amplificationfactor of said limiter amplifying unit.
 7. The noise measuring apparatusaccording to claim 6 further comprising a C/N ratio calculating unit,that calculates a C/N ratio based on a measured result of said carriermeasuring unit and said noise measuring unit.
 8. A noise measuringmethod comprising: a limiter amplifying step of providing a signal to bemeasured in a predetermined range; and a digital data converting step ofconverting the output from said limiter amplifying step into digitaldata.
 9. A computer-readable medium having a program of instructions forexecution by the computer to perform a noise measuring process, saidnoise measuring process comprising: a limiter amplifying step ofproviding a signal to be measured in a predetermined range; and adigital data converting step of converting the output from said limiteramplifying step into digital data.